A conventional baby carriage generally has a front wheel rod 107, an inverted U-shaped push rod 109 connected with the front wheel rod 107 by means of a female joint 108 and a male joint 112, a rear wheel rod 110 pivotally connected with the push rod 109 and a seat rester 111 fixed with the push rod 109, as shown in FIG. 7. A collapsible function is performed by the male and female joint 112, 108 shown in FIG. 8. The female joint 108 fixed on top of the front wheel rod 107 has a hole 1081 in a top surface and a V-shaped groove 1082 in an inner wall, and the male joint 112 fixed on bottom of the push rod 109 has a tenon 1121 extending down to engage the hole 1081, and a projection on a side wall to engage the inverted V-shaped groove 1082, and thus both the male and the female joint 112, 108 lock the front wheel rod 107 and the push rod 109 firmly for use. The collapse it, a grip 1123 of the male joint 112 is to be pulled up, disengaging the tenon 1121 from the hole 1081 and then the push rod 109 can be pulled to collapse downwardly down.